What Wayne said, backing up a vmdk like that is great for bare metal recovery, but it's rubbish for granular stuff. Not least of all because you'd need a new vmdk each night. I know some high end back up software can do some very nifty vmdk aware stuff, but imho, you're far better off backing up 'data' in the same way that you would for a physical server.
One other thing to watch with some kind of live custom vmdk backups is that you're not getting a snapshot, so you need to be wary of what's running. Basically, booting up from a standard copied vmdk would be like booting up from a server that has just had the power pulled.
There's loads on Google (application aware I think the term is), but it doesn't really change your original question.
As an aside, even on VMs we still use DPM to do full restores, but it's more a cost and support issue when we roll out to customers.
EDITED: 30 Oct 2012 23:14 by PILOTDAN